Control apparatus for a powered hoist

ABSTRACT

A control apparatus for a powered hoist which has a winch drum, a variable torque motor for driving the drum, and a brake for the drum, includes a device for detecting the load torque applied by the drum to the brake, when the latter is engaged, a circuit for increasing the torque of the motor and for releasing the brake only when the motor torque exceeds the load torque, and a circuit for varying the motor torque when the brake has been released.

United StatesPatent [191 Maltby et al.

[ CONTROL APPARATUS FOR A POWERED HOIST [75] Inventors: Peter JohnMaltby, Codsall; Stanley George Glaze, Brierlcy Hill; Kenneth HaroldEllis, Wolverhampton; Donald Craven, Wolverhampton; John Michael Binns,Lichfield, all of England l73| Assignce: Lucas Aerospace Limited,

Birmingham, England [22] Filed: Mar. 20, 1973 [21] Appl. No.: 343,047

[ 30] Foreign Application Priority Data Mar. 21, 1972 Great Britain13213/72 [52] US. Cl 187/29 R [51] Int. Cl. G05d 17/02 [58] Field ofSearch 187/29 1451 Nov. 12, 1974 [56] References Cited UNITED STATESPATENTS 3,244,957 4/1966 Spiess ct al. 187/29 X 3,486.10] 12/1969 Rulli187/29 X 3,614,996 10/1971 Saito et a1 187/29 Primary ExaminerRobert K.Schaefer Assistant Examiner--W. E. Duncanson. Jr. Attorney, Agent, or lirmHolman & Stern [57] ABSTRACT 23 Claims, 3 Drawing Figures Z /r34 7/ y160 I 173 l8 -'l l\ PATENIEDnnv 12 1974 SHEET 2 BF 3 p gngmi 3,847,251

MENTE" SHEET 30F 3 1 CONTROL APPARATUS FOR A POWERED HOIST Thisinvention relates'to control apparatus for powered hoists and has anobject to provide such a control apparatus in a convenient form.

' According to theinvention a control apparatus for a means formodifying the second torque when the brake has been released.

An example of the apparatus according to the invention will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 showsas a block a pair of powered hoists together with associatedcontrol apparatus;

FIG. 2 is a diagram of a control apparatus, and

FIG. 3 is a circuit diagram of a part of the control apparatus.

Referring first to FIG. 1, a pair of powered hoist arrangements l0, 11each comprises a winch drum 12 coupled by means of a shaft 13 to a gasturbine 14. A brake assembly 15 is mounted on the shaft 13 to arrest thedrum in a manner later to be described. The turbines l4 and brakeassemblies 15 are substantially as described in our co-pendingapplication No. 1404/72. Brake assemblies 15 are spring-biased to arrestrotation of the drums 12 and are movable to release drums 12 by a gaspressure from a source 16 which also acts to drive turbines 14. Gassupply to each brake assembly 15 is under control of an associatedsolenoid valve 140 ('FIGJZ) responsive to electrical signals on lines 19from-a pair of control apparatuses 17, 18 respectively associated withthe hoist arrangements 10, 11.

Each turbine 14 includes a control valve operable by means of anelectric motor to reverse the direction of rotation of the turbine andalso to control the amount of gas flow through the turbine, and hencethe turbine power output. Electrical signals to control the motors aresupplied from the associated control apparatus via lines 20. Thepositions of the control valves are fed back to the associated controlapparatus via lines 21.

Between each turbine 14 and the gas supply 16 is a shut-off valve 22which is spring-biased to a shut position and which is operable to openby gas pressure from supply 16 under control of a solenoid valve 23.Valves 23 are responsive to signals on lines 24 from the associatedcontrol apparatus to open valves 22.

Each drum 12 is arranged so that associated cables 25 are laid up ondrums 12 in a single layer only. The torque applied to each drum 12 by agiven load W thus remains constant. The brake assemblies 15 respectivelyinclude a load-sensing elements 26, 27 which are operable, when theassociated brake assembly 15 is holding the drum 12, to supply a voltagesignal corresponding to the torque on the drum 12 to the controlapparatus via lines 27a.

Brake assemblies 15 also include microswitches 40, 41 (FIG. 2) operable,when the associated brake assembly 15 is holding its drum 12, to providean electrical signal via line 28 to the control apparatus as soon 2 asthe torque supplied by turbine 14 overcomes the torque due to load W.

Associated with each drum 12 are microswitches 29, 30 (FIG. 2) whichapply voltage control signals-to the associated control apparatus viarespective lines 31, 32 when the drum 12 is at opposite extremes of itstravel, that is when the cable 25 is respectively wound fully in andfully out. Potentiometers 183, 184 (FlG. 2) associated with therespective drums 12, provide signals on lines 33 indicating thepositions of the drums l2, and hence the amounts by which cables 25 arewound in or out.

Each control apparatus l7, 18 includes a respective control panel 34, 35later to be described. Panels 34,

35 conveniently comprise hand-held units arranged so that control may beeffected using one hand only.

The control apparatuses l7, 18 are interconnected in a manner later tobe described, whereby both hoist arrangements 10, 11 may, if required,be controlled from a single one of the panels 34, 35.

Each control apparatus 17, 18 incorporates a plurality of NAND gateswhose input connections are such that both a +5 volt potential and anopen circuit to these connections are logically equivalent to l and anearth potential applied to the connections is logically equivalent to 0.1

Referring to FIG. 2, control apparatus 17 includes pair of switches 36,37 which are respectively connected between positive and negativevoltage sources and a common terminal 38. The winding of a potentiometer39 is connected between terminal 38 and earth. Switches 36, 37 andpotentiometer 39 form part of the control panel 34.

Apparatus 17 includes an end stop circuit 54 to which terminal 38 isconnected. Circuit 54 includes a diode 42 having its cathode connectedto terminal 38 and its anode connected via a resistor chain 43 and aninverter 44 to one input 45a of a NAND gate 45. An intermediate point ofresistor chain 43 is connected via a diode 46 to earth so that a currentcan flow from earth via diode 42 to terminal 38 when the latter is at anegative potential. Input 45b of gate 45 is connected via line 32 andmicroswitch 30 to a +5 volt supply, and via a resistor 47 to earth.

Tenninal 38 is also connected to the anode of a diode 48 whose cathodeis connected via a resistor chain 49 to one input 50a of a NAND gate 50.An intermediate point on resistor chain 49 is connected to earth viaaresistor 9. A second input 50b of gate 50 is connected via line 31 andmicroswitch 29 to a +5 volt supply, and also via a resistor 8 to earth.

The outputs of NAND gates 45, 50 provide two of the inputs of a threeinput NAND gate 51, whose third input is provided in a manner later tobe described. An inverter 52 has as an input the output of gate 51, theoutput of inverter 52 being connected to an output line 66 for the endstop circuit 54.

The wiper of potentiometer 39 is connected via a resistor 55 to theinput terminal of an amplifier 56. The output tenninal of amplifier 56is connected, via resistors 57, 58 in series, to the input terminal of afurther amplifier 59. The common point 60 of resistors 57, 58 isconnected, via diodes 61, 62 respectively. to negative and positivereference voltages of predetermined values. The arrangement of diodes61, 62 is such that if the magnitude of the voltage at point 61 exceedsthat of the reference voltages, current flows in the appropriate diodeto maintain point 60 at the reference voltage.

The output terminal of amplifier 59 is connected to one input terminalof each pair of differential amplifiers 63, 64 whose other inputterminals are respectively connected to negative and positive voltages.The output terminals of amplifiers 63, 64 are commonly connected to thethird input of NAND gate 51 via a line 53.

Amplifiers 56,59, 63, 64 and the associated resistors and diodes form,in conjunction with end-stop circuit 54 a speed and direction selectorcircuit 65, having an output line 67 provided by the output of amplifier59, and whose manner of operation is as follows. Assuming that theassociated drum 12 is not at either end of its travel, switches 29, 30are open. Then if switch 36 is closed to select an upward direction forthe asso ciated hoist, a 1 will appear at input 50a of gate 50. Theinput of inverter 44 is earthed, i.e., volts providing a l at input 45aof gate 45. Since, however, inputs 45b and 50b are both at 0, both gates45, 50 have a 1 output.

Movement of potentiometer 39 to select a hoist speed will causeamplifiers 63, 64 to provide a positive output signal. All inputs togate 51 will thus be at 1 and gate 51 will have a 0 output, which isconverted to a l on line 66 by inverter 52. If however, switch 29 isclosed indicating that the hoist is at the top limit of 50 to have an 0-output. Gate 52 will then provide a 0 output on line 66. M I

- In a'simil'ar manner gate 45 will have an 0 output when switches 30,37 are both closed, and will have a 1 output in other conditions. A lsignal thus appears on an output line from circuit 65 only when a speedand direction isfseleeted and the hoist is also free to move intheselected direction; If both switches 36, 37 are open, then both gates45, 50 will have a 1 output. lnthis circumstance a l on line 53 derivedin a manner to'be described later, will result in a 1 output on line 66from end stop circuit 54.

Lines 68, 69 are connected to the input terminals of amplifiers 56,59respectively. Lines 68, 69 carry signals which are more or less positiveor negative when the selected direction is respectively up or down. The

- signal online 68 is not subjectto the speed limitation imposed bydiodes 61, 62.

Microswitch 40 is connected between a 5 volt supply and the signal line28. A brake indicator latching circuit 70 comprises NAND gates 71, 72.Line 28 is connected to one input 71a of gate 71. Input 71a is alsoconnected via a resistor to earth. The output of gate 71 is connected toan input 72a of gate 72, whose other input 72b is connected to alatching circuit reset line 73. The output of gate 72 is connected to aninput 71b of gate 71. Microswitch 40 is operated by brake 15, when thelatter is engaged with the associated winch drum 12, so that when atorque applied by the turbine 14 overcomes the torque due to load W,microswitch 40 opens.

Assume initially that there is an 0 on line 73 and that microswitch 40is closed-The output of gate 72 will be at l and this last signalcombines with the 1' from switch 40 to set the output of gate "71 to 0.The

state of circuit 70 does not, therefore, change if the signal on line 73becomes l lf with signal on line 73 at l the microswitch 40 opens, theoutput of gate 71 becomes 1 and the output of gate 72 becomes 0. Thislast 0' output is also applied to gate 71 to latch the out; put of gate72. Circuit thus has an 0 output only Switching circuit 78 forms part ofa power-demand indicating circuit 79 and has a pnp transistor 80 withits base connected to connection 77, via a resistor 81. The emitter andcollector of transistor 80 are respectively connected to a +5 voltsupply and, via a resistor 82, to a 12 volt supply. The collector oftransistor 80 is also connected via a resistor 83 to the gate of a fieldeffect transistor 84. The source of transistor 84 is connected to earth.A positive potential at connection 77 cuts ofi' transistor 80, applyingl2 volts to the gate of transis tor 84, which then becomesnon-conductive. Similarly, an earth potential at connection 77 causestransistor 84 to conduct.

Circuit 79 also includes an amplifier 85 which receives an input fromthe load sensing device 26 on the associated brake assembly 15. Theoutput terminal of amplifier 85 is connected to the drain of transistor84. A tacho-generator 86 is responsive to the speed of the associateddrum 12. The drain of transistor 84 and tacho-generator 86 are connectedby respective resistors 87, 88 to an output terminal 89 of circuit 79.

The output line'67 of circuit'65 is connected via resistors 90, 91 tothe output terminal 89 of circuit 79. Terminal 89 also forms the inputterminal of a position control circuit 93 for a synchro motor 94, whichoperates the direction and speed control valve in the turbine 14.

Circuit 93 includes an amplifier 95, to the input terminal of which theterminal 89 is connected. The out I common point of resistors 102, 103is connected to earth via a switching circuit 104, identical withcircuit 78 previously described.

A latching circuit 105, identical with latching circuit 70, isresponsive both to the output from gate 75 and to the signal on line 73.A signal on a line 106 between the output of circuit and a controlconnection 107 for switching circuit 104 is thus maintained at l whenthere is an 0 output from gate 75.

A pair of switches 110, 111 are included in the respective controlpanels 34, 35. Panels 34, 35 also respectively include potentiometers112, 113 and associated respective spring-loaded switches 114, 115.Switch 114 is connected between a +5 volt supply and an inverter 116which forms part of a synchronising control circuit 117. The input ofinverter 116 is also connected via a resistor to earth. Switch 114 andpotentiometer 112 may be adjusted, in a manner later to be described, toobtain a condition in which both drums 12 are moved in unison but withdifferent amounts of their associated cables wound out. Switches 110,111 are connected between a +5 volt supply and one input of a NAND gate118 whose other input is connected to the output of inverter 116. Theoutput of gate 118 is connected via inverter 119 to one input of aNANDgate 120. The output of gate 120 is connected to one input of a NANDgate 121 and the output of gate 121 is connected via an inverter 122 toa line 123 which provides an output connection for synchronising circuit117 as a whole. Circuit 117 also includes an inverter 124 which isconnected between output line 74 from latching circuit 70 and a secondinput of gate 120. A NAND gate 125 has one input also connected to theOutput of gate 124 and a second input connected to the output of gate118. A further output line 126 for circuit 117 extends from the outputof inverter 119. Synchronising circuit 117 also includes a latchingcircuit 164 identical with circuit 70 and including NAND gates 165, 166.One input of gate 165 is connected to earth via a resistor and also viaone of lines 28 and microswitch 41 to a +5 volt supply. A reset line 167for circuit 164 is connected to control apparatus 18 and corresponds toline 73 in apparatus 17. Signals on lines 73, 167 are obtained in amanner later to be described.

The output of latching circuit 164 is connected via an inverter 129 to athird input of gate 120, and also via a line 163 to one input of a gate(not shown) in apparatus 18 and corresponding to gate 75 abovedescribed.

Line 123 is connected via an inverter 130 to one input of a NAND gate131, whose other input is connected to the output line 66 from circuit65. The output of gate 131 is connected via an inverter 132 to thecontrol connection 133 of a switching circuit 134 which is identical toswitching circuit 78. Circuit 134 is operable to connect the commonpoint of resistors 90, 91 to earth, and circuit 134, together withinverters 130, 132 and gate 131, comprises an output control circuit 135for signals on line 67 from speed selection circuit 65. End stop circuit54 and circuit 135 together comprise a switching arrangement forisolating a speed and direction demand signal from the position controlcircuit 93.

A solenoid 140 for the gas control valve for the brake is responsive toa brake control circuit 141, comprising a NAND gate 142, an inverter146, a latching circuit 147, identical with circuit 70, and power stageswitching circuit 148, identical with circuit 78. Control circuit 141has as its inputs the lines 66 and 123 and a third input provided by adifferential amplifier 145 responsive to the output of thetacho-generator 86. Amplifier 145 is biased so as to provide a 1 outputwhen the drum 12 is stopped, and an 0 output when drum 12 is rotating.

A reset circuit 128 is also responsive to an output signal fromamplifier 145 and comprises NAND gates 144, 154, 155, 157 159, andinverters 143, 153, 158, 160, 169.

Line 66 is connected to one input of gate 142 and via inverter 143 toone input of gate 144. Gates 142, 144 also have inputs provided bydifferential amplifier 145. Line 123 is connected via inverter 146 to athird input of gate 142. The output of gate 142 is connected, vialatching circuit 147, to a control connection of the power stage 148.Stage 148 is in series with relay contacts 149 to control current flowfrom a 28 volt supply through solenoid 140. As above described theturbine 14 includes a gas shut-off valve 22. The shut-off valve 22 iscontrolled by a servo-valve 23 operable by a solenoid 150 which isconnected in parallel with solenoid and stage 148. Solenoid is not,however, responsive to control circuit 141, but to operation of relaycontacts 149 as a result of operation of a relay 151 by either of a pairof emergency stop switches 138, 139 on the respective panels 34, 35.

The output of gate 144 is connected via inverter 153 to one input ofeach of gates 154, 155. Output line 126 from circuit 117 is connected tothe other input of gate 155, to one input of gate 157 and via inverter158 to an input of gate 154. The outputs of gates 154, 155, 157 provideinputs for gate 159. A further input for gate 159 is provided from a +5volt supply when either of switches 138, 139 in panels 34, 35respectively are made. The output of gate 159 is connected via inverter160 to the reset line 73, which forms an output line from reset circuit141. Line 73 provides an input into one gate of each latching circuit70, 105 and 147, as described above.

A switching circuit 161, identical to circuits 78, 104, 134 is operable,when an earth potential is applied to its control connection 162, toconnect the common point of resistors 98, 99 to earth. Connection 162 isconnected to the output of inverter 132 in circuit 135. A line 168 isconnected, via an inverter 169 to a second input of gate 157. Line 168is connected, in apparatus 18, to the output of a gate which correspondsto gate 144 as described above. The output gate 144 is similarlyconnected, via a line 179 to an inverter in apparatus 18 correspondingto inverter 169.

The parts of the control apparatus 17 so far described are thesenecessary to effect control of the associated hoist arrangement 10 only,by means of the control panel 34, in which cases switches 110, 111 willnot be made, and there will always be a 0 on line 126. Before startingoperation the amplifier 145 has a 1 output, and if speed and directionhave not been selected there is a 0 on line 66 from circuit 65. Bothinputs of gate 144 are therefore at l and the resulting 0 at the outputis inverted to provide a l at one of the inputs of gate 154. The otherinput of gate 154 is also at l as a result of the inverted 0 on line126. The output of gate 154 is thus at 0 producing a l at the output ofgate 159 and a 0 on reset control line 73. The outputs of all thelatching circuits 70, 105, 147 are thus at l, irrespective of the statesof the other inputs of these latching circuits.

The 0 on line 66 causes the output of gate 142, and hence that oflatching circuit 147, to be 1 causing the switching circuit 148 tode-energise brake solenoid 140. The brake assembly 15 is thus holdingthe shaft 13.

If, however, there is a l on line 66 and an-O on line 126, all theinputs of gate 159 will be at l The signal on line 73 is thus, in thiscondition, not affected by the signal on line 168 from apparatus 18. If,however, there is a l on line 126, i.e., synchronised operation selectedby either of switches 110, 111 and switches 114, 115 are in theirnormally open condition, the output of gate 157 will be 1 only if theinput to gate 169 is also 1. The input to gate 169 is 1' only when theoutput of the gate in apparatus 18, corresponding to gate 144', is 1,that is when the output of the end stop circuit in apparatus 18 is 1.When synchronised operation is selected, i.e., when there is a l on line126, the reset circuit in apparatus 18 will have a 1 output only whenend stop circuit 54 in apparatus 17 has a 1 output.

Selection of a speed and direction provides a l on line 66 which, byapplying an to one input of gate 144, causes the output of the latter tobecome 1. An 0 is thus applied to one input of gate 154, causing itsoutput to become 1. The states of gates 155, 157 remain unchanged, andthe output of gate 159 therefore becomes 0. The signal on line 73 isthus l, whereby the states of latching circuits70, 105, 147, may bechanged.

Assuming initially that the brake assembly is hold ing drum 12 againstthe load W, there is a l on line 74 from latching circuit 70 as abovedescribed. This l is inverted and causes gate 125 to have a 1 output.The 0 remaining on line 126 is inverted by inverter 120, and the two 1inputs to gate 121 cause the latter to have an 0 output which isinverted to provide a 1 on line 123. An 0 is applied to one input ofgate 131, and the resultant 1 output is inverted to cause switchingcircuit 134 to earth the common point of resistors 90, 91. A speed anddirection demand signal from circuit 65 is thus earthed. The commonpoint of resistors 98, 99 is also earthed by circuit 61.

The l on each of lines 66, 74 causes the output of is thus applied toterminal 89 of position control circuit 93. Since the common point ofresistors 98, 99 is *earthed the torque load signal appearing atterminal 89 is routed to amplifier 97. The 0 at the output of gate 75also causes latching circuit 105 to maintain a 0 at the controlconnection of switching circuit 104, earthing the common point ofresistors 102, 103. Capacitor 101 thus provides the feedback path foramplifier 97, causing the latter to act as an integrator. The inputsignal to amplifier 100 thus increases at a rate dependent on themagnitude of the torque sensed by element 26. Motor 94 thus operates toincrease the torque delivered by turbine 14.

When the turbine torque exceeds the torque due to load W, brake assembly15 is rotated against the load by shaft 13, and microswitch 40 becomesopen circuit. The resultant 0 at the input of latching circuit 70 causesan 0 to be set on line 74, and also causes the signals at both inputs ofgate 125 to become l The resulting O on one input of gate 121 places an0 on line 123. All inputs to gate 142 then become l and circuit 147latches an 0 on to the switching circuit 148, energising solenoid 140and releasing the brake assembly 15 from the shaft 13.

The 0 on line 74 is inverted by gate 75 and is applied to latchingcircuit 105, which does not, however, change its state. Switchingcircuit 104 thus remains in its closed circuit condition and amplifier97 continues to integrate. The 1 from gate 75 is again inverted andswitching circuit 78 earths the output from load sensing element 26.

The 0 on line 123 causes both inputs to gate 131 to be 1 and theresulting 1 output from inverter 132 places switching circuits 134, 161in their open circuit condition. The speed and direction demand signalfrom circuit 65 can thereby pass to terminal 89 to be summed with theoutput of tacho-generator 86 to provide a speed error signal. Theamplified signal from terminal 89 can also pass via resistors 98, 99 toamplifier 100. A potentiometer 181 is responsive to the position of theair control valve for turbine 14 in hoist arrangement 10. The voltage onthe wiper of potentiometer 181 is supplied via line 21 and a resistor tothe input of amplifier 100.

The input signal to amplifier is thus a positionerror signal for the aircontrol valve.

In the absence of a speed error signal at terminal 89 the integratingamplifier 97 has an output signal which remains at the level at whichload torque was overcome. In this condition the motor 94 has positionedthe air control valve so the turbine torque balances load torque and thehoist is stationary. A speed-error signal at terminal 89, correspondingto a requirement for upward movement of the load, causes the outputsignal from amplifier 97 to increase at a rate corresponding to themagnitude of the speed-error signal. This increasing signal is summed atthe input of amplifier 100 with the output of amplifier 95, and with thefeedback signal from potentiometer 181, to provide a freshposition-error signal which reduces to zero as the air control valve ismoved by motor 94.

A speed-error signal corresponding to a downward movement of the loadsimilarly causes the input signal to amplifier 100 to be reduced, andmotor 94 moves the air control valve so that the torque output of theturbine falls below that imposed by the load W. The winch is thusrotated by the load against the reduced lifting torque of the turbine. v

If there is no external load on the cable, the weight of the cable whichremains off the drum, even in the wound in position, is sufficient toprovide a torque load signal at terminal89. The turbine torque thusincreases until the brake is released, as before. The voltage level atthe output of integrating amplifier 97 is nevertheless small and adownward speed-error signal causes motor 94 to drive the gas controlvalve to reverse the direction of rotation of the turbine.

If the turbine is stopped, either by movement of potentiometer 39 to azero-speed position or by opening switches 36, 37, an 0 appears at theoutput of end-stop circuit 54 and is applied via line 66 to resetcircuit 128, causing the signal on line 73 to change from l to 0. The 0on line 73 is applied to one input of each of latching circuits 70, 105,148 whose outputs are then set to l irrespective of the signals at theother inputs of these latching circuits. The 1 output of circuit 70 isapplied to synchronising circuit 117 and causes the signal on line 123to change from 0 to l. The l on line 123 and the O on line 73 are eachsufficient to cause brake control circuit 141 to apply the brake. At thesame time the output of inverter 76 is set to 0 and switching circuit 78conducts, earthing the output of load-sensing element 26. The l on line123 operates via output control circuit 135 to cause switching circuit134 to earth the junction of resistors 90, 91, and also operates tocause switching circuit 161 to earth the junction of the resistors 98,99. Finally, the l output from latching circuit renders switchingcircuit 104 non-conductive, and amplifier 97 ceases to act as anintegrator. The signal level from amplifier 97 thus disappears.Apparatus 17 is thus set to its pre-start condition, from which itcannot depart until there is once again a 1 from end-stop circuit 54.

If, while hoist arrangement 10 is running, either of emergency stopswitches 138, 139 is opened, relay 151 is de-energised and contacts 149open. Solenoids 150 and 140 are in consequence de-engergised and thebrake is applied. At the same time the input to gate 159 causes an 0 tobe set on line 173. The output of all latching circuits 70, 105, 147thus becomes l and the apparatus is reset, as before to its pre-startcondition.

The input of amplifier 56 is connected via a resistor 170 to earth via aswitching circuit 171 which is identical to circuit 78. The controlconnection of circuit 171 is connected to a volt supply via the switches110, 111. The common point of resistor 170 and circuit 171 is alsoconnected via a resistor 172 to a line 173 which extends to the wiper ofa speed demand potentiometer 174 forming part of control panel 35.Apparatus 18 is identical to apparatus 17 as above described, exceptthat apparatus 18 has no equivalent of synchronising control circuit117.

A synchronising circuit 180 is connected to apparatuses 17, 18, tocontrol panels 34, 35 and via lines 33 to the potentiometers 183, 184respectively associated with the drums 12.

In the convention of the diagram of FIG. 2 upward movement of the wipersof potentiometers 183, 184 corresponds to rotation of the associateddrums to provide upward movement of a load thereon. The wiperpotentiometer 183 is connected via a resistor 185,an inverting amplifier186 and a further resistor 187 to a summing junction 188. The wiper ofpotentiometer 184 is connected via a resistor 182 to junction 188. Thewipers 112a, 113a of potentiometers 112, 113 are also connected tojunction 188. Wipers 112a, 113a are biased towards the mid-points oftheir respective tracks. Associated with wipers 112a, 113a are latchingmeans indicated at 189, 190, for retaining these wipers in requiredpositions. Operation of the latching means 189, 190 to disengage therespective wipers 112a, 113a causes'the associated switches 114, 115 tobe closed.

Summing junction 188 provides an input connection for an amplifier 191whose output terminal is connected to earth via a resistor 192 and aswitching circuit 193, identical to switching circuit 78. The commonpoint of resistor 192 and circuit 193 is connected via a line 206 and aresistor 207 to the input of amplifier 59. The output terminal ofamplifier 191 is also connected to earth via a resistor 194, aninverting amplifier 195 a further resistor 196 and a further switchingcircuit 197. The common point of resistor 196 and circuit 197 isconnected via a line 208 to a part of control apparatus 18 correspondingto resistor 207 and amplifier 59.

Load sensing element 26 is connected via an amplifier 198 to one inputof a differential amplifier 199. Load sensing element 27, associatedwith hoist arrangement l l, is connected via an amplifier 200 to theother input of amplifier 199. Amplifier 199 is such that when the loadsare equal or that sensed by element 26 is the greater there is, an 0 atthe output of amplifer 199, and when the load sensed by element 27 isthe greater there is a l at the amplifier output.

The output of amplifier 199 is connected to one input of a NAND gate 201and via an inverter 202 to one input of a NAND gate 203. The otherinputs of gates 201', 203 are connected to the +5 volt supply viaswitches 110, 111. The output of gate 201 is connected via an inverter204 to the control connection of switching circuit 193. The output ofgate 203 is connected via an inverter 205 to the control connection ofswitching circuit 197.

A switching circuit 209 forming part of control apparatus 18 has itscontrol connection connected to the +5 volt supply via switches 110,111. A pair of resistors 210, 211 also form part of apparatus 18 and areconnected in series in a line 212 between the wiper of potentiometer 39and the input connection of an amplifier 213 which also forms part ofapparatus 18 and corresponds to amplifier 56 in apparatus 17. Resistors170, 172, 210, 211 have the same value. This value is twice that ofresistors 55 in apparatus 17 and also twice that of a resistor 214 atthe input of amplifier 213 in apparatus 18. The impedance between thewiper of potentiometer 39 and the amplifier 56 is the same as thatbetween potentiometer 39 and amplifier 213, when switching circuit 171is open. Similarly the impedance between potentiometer 171 andamplifiers 56 and 213 are the same when switching circuit 209 is open.

In use, with either one of switches 110, 111 made, a 1 is applied to oneinput of gate 118. If switches 114, are open, there is also a 1 at theother input of gate 118. The resulting 0 output from gate 118 causes theoutput of gate 125 to be at l even after the torque load on hoistarrangement 10 has been overcome and microswitch 40 has opened. Since atleast one of the inputs of gate 121 must be at 0 if there is to be an 0on line 123 to allow the hoist to start, all the inputs to gate must beat l This last condition will only obtain when the output of latchingcircuit 164 is at 0, i.e., when the torque load on hoist arrangement 11has also been overcome.

Assume, in use, thatboth hoist arrangements 10, 11 are to be controlledfrom control panel 34, and assume also that the load W on hoistarrangement 11 is the heavier. There will then be, as above described, a1 output from the amplifier 199. Both inputs of gate 201 are thus at 1and the resulting l at the control connection of switching circuit 193causes the latter to be open-circuit. The l output from amplifier 199 isinverted by inverter 202 and causes the output of inverter 205 to beat0. Switching circuit 197 thus earths the output of amplifier 95, andthere is no signal on line 208. A signal from amplifier 191 is thusapplied via line 206, and resistor 207 to the input of amplifier 59 inapparatus 17.

When switch 110 or 111 is closed, both switching circuits 171, 209 arerendered open-circuit. The inputs of amplifiers 56 and 213 in apparatus17 and 18 respectively are thus inter-connected via resistors 170, 172,210, 211. A speed and direction selected on either of control panels 34,35 will be applied to both of control apparatuses 17, 18. As describedabove with reference to the operation of end-stop circuit 54, even ifboth direction selection switches on the associated panel 34 or 35 areopen, a speed and direction signal at the inputs of amplifiers 56, 213applies a l to line 53 and to the corresponding line in apparatus 18,thereby causing the output signal from the associated end-stop circuitsto be 1. Neither of hoist arrangements 10, 11 will, however, start upuntil the torque load on both has been overcome, as described above inconnection with the synchronising circuit 117 of apparatus 17.

With both hoists operating to lift their loads, and the load on hoistarrangement 1 1 being the heavier, it is to be expected that drum 12 inarrangement 10 will lead the drum of arrangement 11. The wiper ofpotentiometer 183 thus becomes more positive than that of potentiometer184. The input of amplifier 191 becomes negative and a negative signalis applied via line 206 to the input of amplifier 59. This negativesignal opposes the signal from control panel 34 by an amount dependenton the amount by which the drum arrangement 10 leadsthat of arrangement11.

Similarly, if arrangement 10 lags behind arrangement 11, the'speeddemand signal from control panel 34 is enhanced by the signal on line206. It will be understood thatif the loads are being lowered theoperation of the apparatus is substantially the same, the signal on line206 opposing any tendency of hoist arrangement 10 to lag or leadarrangement 11. It will also be understood that if the load arrangementon 10 is the same as that on arrangement 11 or is the heavier, signalsare then applied via line 208 to apparatus 18 to reduce any tendency ofhoist arrangement 11 to lag or lead arrangement 10. In general thearrangement having the lighter load is caused to follow that having theheavier load. With loads swinging the heavier load may alternate betweenarrangement 10, 11 and the functions of master and slave apparatus thenalternate between apparatus 17 and apparatus 18 under control ofswitching circuits 193, 197.

If when arrangements 10, 11 are being operated in synchronism, it isrequired that, say the drum 12 in arrangement 10 is to be moved withrespect to the other drum, this may be effected by adjustment of eitherpotentiometer 112 or potentiometer 113 in the respective control panels34, 35. Disengagement of the latching means '189 to move potentiometer112 causes switch 114 to be made. The resulting at the output ofinverter 116 causes the output of gate 118 to be l The effect on circuit117 is thus as if switches 110, 111 were not closed, while switch 114 orswitch 115 are closed.

' lf wiper 1 12a is moved a desired amount from its central position theassociated interlock 189 is then released to maintain the position ofwiper 112a, thereby re-opening switch 114. As a result of movement fromits central position wiper 112a cause a biasing voltage to be applied tojunction 188. If the load on hoist arrangement 11 is the greater, thenthis biasing voltage is applied to the'input of amplifier 59 inapparatus 17. If the biasing voltage is positive then, when the hoistarrangements are started by selection of a speed and direction by eitherof panels 34, 35, this positive bias will increase the upward speed ofhoist arrangement until balanced by the increasing negative bias duetothe difference in the positions of potentiometers 183, 184 after whichboth hoists move in synchronism. Similarly, if the load on arrangement10 is the heavier, then a positive voltage from potentiometer 112applies a negative bias via amplifier 195 and switching circuit 197 tothe input of an amplifier in apparatus 18, corresponding to amplifier 59in apparatus 17. Once again hoist arrangements 10, 11 are driven atdifferent speeds until the signal at junction 188 is zero, both hoistsmoving in synchronism thereafter.

We claim:

l. A control apparatus for a powered hoist having a winch drum, a motorcapable of variable output for driving the drum and a brake for thedrum, said control apparatus comprising means for detecting a firsttorque applied by the drum to the brake when the latter is en gaged toarrest the drum, control means for causing a second torque supplied bysaid driving motor to be increased, brake control means responsive tomovement of said drum by said second torque, said brake control meansfor releasing said brake only when the second torque exceeds the firsttorque, and further control means, operative only when the brake hasbeen released, for modifying the second torque.

2. A control apparatus for a powered hoist having a winch drum, a motorcapable of variable output for driving the drum and a brake for thedrum, said control apparatus comprising means for generating a firstelectrical signal dependent on a first torque which is applied by thedrum to the brake when the latter is engaged to arrest the drum, meansresponsive to the magnitude of said first electrical signal to generatea second electrical signal, said motor supplying a second torque, meansfor increasing said second torque at a rate dependent on the magnitudeof said second electrical signal, means for releasing said brake onlywhen the second torque exceeds the first torque, and furthercontrolmeans, operative only when the brake has been released, for modifyingthe second electrical signal.

3. An apparatus as claimed in claim 2 which includes a synchro motorresponsive to said second electrical signal to vary said second torquefrom said driving motor.

4. An apparatus as claimed'in claim 3 in which said means for releasingthe brake comprises afirst'switching means, operable by the brake, whena part-thereof is urged against said first torque by said second torque,to provide a third electricalsignal, said brake being released inresponse to said third electrical signal.

5. An apparatus as claimed in claim 4 which includes second switchingmeans responsive to said third electrical signal to provide a fourthelectrical signal, and an electro-magnet device responsive to saidfourth electrical signal to release said brake. f

6. An apparatus as claimed in claim 5 which'includes third switchingmeans responsive to said third electrical signal to isolate'said firstelectrical signal from said second electrical signal generating means.

7. An apparatus as claimed in claim 5 which includes means forgenerating a fifth electrical signal dependent on the rotational speedof said drum, said means for generating the second electrical signalbeing responsive to said fifth electrical signal. r

8. An apparatus as claimed in claim 7 in which said means for modifyingthe second torque includes means for generating a sixth electricalsignal dependent on a desired speed and direction-of rotation of saiddrum, said means for generating the second electrical signal beingresponsive to said sixth electrical signal.

9. An apparatus as claimed in claim 8 which includes fourth switchingmeans operable when said drum has reached a permitted limit of itsrotation in either direction, for isolating said sixth electrical signalfrom said second electrical signal generating means.

' 10. An apparatus as claimed in claim 9 in which said second electricalsignal generating means includes means for summing said fifth and sixthelectrical signals and a first amplifier responsive to the output ofsaid summing means to provide an eighth electrical signal.

11. An apparatus as claimed in claim in which said second electricalsignal generating means includes a further amplifier responsive to saideighth electrical signal and to the output of said summing means toprovide said second electrical signal.

12. An apparatus as claimed in claim 11 which includes means forgenerating a feedback signal dependent on the rotational position ofsaid synchro motor, said further amplifier also being responsive to saidfeedback signal.

13. An apparatus as claimed in claim 12 which includes fifth switchingmeans responsive to said third electrical signal to isolate said furtheramplifier from the output of said summing means, whereby said furtheramplifier is responsive only to said eighth electrical signal only whensaid first switching means is not operated by said brake.

14. An apparatus as claimed in claim 11 which includes a feedbackarrangement associated with said first amplifier to cause the latter tooperate as an integrator, and sixth switching means responsive tooperation of said sixth electrical signal generating means and tooperation of said fourth switching means to render said feedbackarrangement operative, whereby said first amplifier acts as anintegrator when said sixth electrical signal is present and when saiddrum is not at one of its limits of angular rotation.

15. An apparatus as claimed in claim 14 which includes a logic circuitresponsive to said fifth electrical signal and to operation of saidfourth switching means and said sixth electrical signal generatingmeans, to generatev a ninth electrical signal, whereby said ninthelectrical signal is present only in the presence of said sixthelectrical signal and when said drum is not at one of its limits ofrotation, and a plurality of latching circuits responsive to said ninthelectrical signal to cancel said third and fourth electrical signals andto cause said sixth switching means to render said feedback arrangementinoperative.

16. An apparatus as claimed in claim 15, in combination with a further,similar, control apparatus for a further powered hoist, similar to thefirst-mentioned hoist, and an interconnection arrangement energisable tocause said control apparatus to coact, whereby the second torquesupplied by both of said driving motors may be modified by the torquemodifying means of one of said control apparatuses.

17. A combination as claimed in claim 16 which includes seventhswitching means operable to provide a tenth electrical signal, saidinterconnection arrangement being responsive to said tenth electricalsignal to cause said control apparatuses to coact.

18. A combination as claimed in claim 17 in which said interconnectionarrangement includes a second logic circuit responsive to said thirdelectrical signal and to said tenth electrical signal to provide aneleventh electrical signal, said fourth switching means and acorresponding switching means in said further control apparatus beingresponsive to said eleventh electrical signal, whereby, when saidseventh switching means is operated, and said first switch means and acorresponding switching means in said further apparatus is operated,said sixth electrical signal, and a corresponding arrangementinoperative.

20. A combination as claimed in claim 19 in which said interconnectionarrangement includes first and second means responsive to the rotationalpositions of the respective drums to provide thirteenth and fourteenthelectrical signals, second summing means responsive to said thirteenthand fourteenth electrical signals to provide a fifteenth electricalsignal, and first and second modifying means for respectively modifyingsaid sixth electrical signal, and a corresponding signal in said furthercontrol apparatus, in accordance with said fifteenth electrical signal.

21. A combination as claimed in claim 20 which includes means forgenerating a sixteenth electrical signal dependent on the torque appliedby the drum of said further hoist to the brake thereof when the latteris engaged, and ninth and tenth switching means responsive to said firstand sixteenth electrical signals and to said tenth electrical signal andrespectively operable to isolate said fifteenth electrical signal fromsaid sixth electrical signal and from the corresponding signal in saidfurther control apparatus.

22. A combination as claimed in claim 20 which includes means formodifying said thirteenth and fourteenth electrical signals inaccordance with a desired difference in the rotational positions of saiddrums.

23. A combination as claimed in claim 17 which includes means forinterconnecting said sixth electrical signal generating means and thecorresponding generating means in said further control apparatus, andeleventh switching means responsive to said tenth electrical signal torender said interconnecting means inoperative.

1. A control apparatus for a powered hoist having a winch drum, a motorcapable of variable output for driving the drum and a brake for thedrum, said control apparatus comprising means for detecting a firsttorque applied by the drum to the brake when the latter is engaged toarrest the drum, control means for causing a second torque supplied bysaid driving motor to be increased, brake control means responsive tomovement of said drum by said second torque, said brake control meansfor releasing said brake only when the second torque exceeds the firsttorque, and further control means, operative only when the brake hasbeen released, for modifying the second torque.
 2. A control apparatusfor a powered hoist having a winch drum, a motor capable of variableoutput for driving the drum and a brake for the drum, said controlapparatus comprising means for generating a first electrical signaldependent on a first torque which is applied by the drum to the brakewhen the latter is engaged to arrest the drum, means responsive to themagnitude of said first electrical signal to generate a secondelectrical signal, said motor supplying a second torque, means forincreasing said second torque at a rate dependent on the magnitude ofsaid second electrical signal, means for releasing said brake only whenthe second torque exceeds the first torque, and further control means,operative only when the brake has been released, for modifying thesecond electrical signal.
 3. An apparatus as claimed in claim 2 whichincludes a synchro motor responsive to said second electrical signal tovary said second torque from said driving motor.
 4. An apparatus asclaimed in claim 3 in which said means for releasing the brake comprisesa first switching means, operable by the brake, when a part thereof isurged against said first torque by said second torque, to provide athird electrical signal, said brake being released in response to saidthird electrical signal.
 5. An apparatus as claimed in claim 4 whichincludes second switching means responsive to said third electricalsignal to provide a fourth electrical signal, and an electro-magnetdevice responsive to said fourth electrical signal to release saidbrake.
 6. An apparatus as claimed in claim 5 which includes thirdswitching means responsive to said third electrical signal to isolatesaid first electrical signal from said second electrical signalgenerating means.
 7. An apparatus as claimed in claim 5 which includesmeans for generating a fifth electrical signal dependent on therotational speed of said drum, said means for generating the secondelectrical signal being responsive to said fifth electrical signal. 8.An apparatus as claimed in claim 7 in which said means for modifying thesecond torque includes means for generating a sixth electrical signaldependent on a desired speed and directioN of rotation of said drum,said means for generating the second electrical signal being responsiveto said sixth electrical signal.
 9. An apparatus as claimed in claim 8which includes fourth switching means operable when said drum hasreached a permitted limit of its rotation in either direction, forisolating said sixth electrical signal from said second electricalsignal generating means.
 10. An apparatus as claimed in claim 9 in whichsaid second electrical signal generating means includes means forsumming said fifth and sixth electrical signals and a first amplifierresponsive to the output of said summing means to provide an eighthelectrical signal.
 11. An apparatus as claimed in claim 10 in which saidsecond electrical signal generating means includes a further amplifierresponsive to said eighth electrical signal and to the output of saidsumming means to provide said second electrical signal.
 12. An apparatusas claimed in claim 11 which includes means for generating a feedbacksignal dependent on the rotational position of said synchro motor, saidfurther amplifier also being responsive to said feedback signal.
 13. Anapparatus as claimed in claim 12 which includes fifth switching meansresponsive to said third electrical signal to isolate said furtheramplifier from the output of said summing means, whereby said furtheramplifier is responsive only to said eighth electrical signal only whensaid first switching means is not operated by said brake.
 14. Anapparatus as claimed in claim 11 which includes a feedback arrangementassociated with said first amplifier to cause the latter to operate asan integrator, and sixth switching means responsive to operation of saidsixth electrical signal generating means and to operation of said fourthswitching means to render said feedback arrangement operative, wherebysaid first amplifier acts as an integrator when said sixth electricalsignal is present and when said drum is not at one of its limits ofangular rotation.
 15. An apparatus as claimed in claim 14 which includesa logic circuit responsive to said fifth electrical signal and tooperation of said fourth switching means and said sixth electricalsignal generating means, to generate a ninth electrical signal, wherebysaid ninth electrical signal is present only in the presence of saidsixth electrical signal and when said drum is not at one of its limitsof rotation, and a plurality of latching circuits responsive to saidninth electrical signal to cancel said third and fourth electricalsignals and to cause said sixth switching means to render said feedbackarrangement inoperative.
 16. An apparatus as claimed in claim 15, incombination with a further, similar, control apparatus for a furtherpowered hoist, similar to the first-mentioned hoist, and aninterconnection arrangement energisable to cause said control apparatusto coact, whereby the second torque supplied by both of said drivingmotors may be modified by the torque modifying means of one of saidcontrol apparatuses.
 17. A combination as claimed in claim 16 whichincludes seventh switching means operable to provide a tenth electricalsignal, said interconnection arrangement being responsive to said tenthelectrical signal to cause said control apparatuses to coact.
 18. Acombination as claimed in claim 17 in which said interconnectionarrangement includes a second logic circuit responsive to said thirdelectrical signal and to said tenth electrical signal to provide aneleventh electrical signal, said fourth switching means and acorresponding switching means in said further control apparatus beingresponsive to said eleventh electrical signal, whereby, when saidseventh switching means is operated, and said first switch means and acorresponding switching means in said further apparatus is operated,said sixth electrical signal, and a corresponding signal in said furtherapparatus, are respectively isolated from said second electrical signalgenerating means and from a corResponding generating means in saidfurther apparatus.
 19. A combination as claimed in claim 18 whichincludes eighth switching means, corresponding to said first switchingmeans and operable by the brake of said further powered hoist to providea twelfth electrical signal, and in which said second logic circuitincludes a further latching circuit responsive to said ninth and twelfthelectrical signals to render said interconnection arrangementinoperative.
 20. A combination as claimed in claim 19 in which saidinterconnection arrangement includes first and second means responsiveto the rotational positions of the respective drums to providethirteenth and fourteenth electrical signals, second summing meansresponsive to said thirteenth and fourteenth electrical signals toprovide a fifteenth electrical signal, and first and second modifyingmeans for respectively modifying said sixth electrical signal, and acorresponding signal in said further control apparatus, in accordancewith said fifteenth electrical signal.
 21. A combination as claimed inclaim 20 which includes means for generating a sixteenth electricalsignal dependent on the torque applied by the drum of said further hoistto the brake thereof when the latter is engaged, and ninth and tenthswitching means responsive to said first and sixteenth electricalsignals and to said tenth electrical signal and respectively operable toisolate said fifteenth electrical signal from said sixth electricalsignal and from the corresponding signal in said further controlapparatus.
 22. A combination as claimed in claim 20 which includes meansfor modifying said thirteenth and fourteenth electrical signals inaccordance with a desired difference in the rotational positions of saiddrums.
 23. A combination as claimed in claim 17 which includes means forinterconnecting said sixth electrical signal generating means and thecorresponding generating means in said further control apparatus, andeleventh switching means responsive to said tenth electrical signal torender said interconnecting means inoperative.